Catalyst composition

ABSTRACT

A catalyst composition comprising (i) a crystalline aluminosilicate selected from the group consisting of zeolite ZSM-5, zeolite ZSM-11, zeolite ZSM-12, zeolite ZSM-35 and zeolite ZSM-38 and having a silica/alumina mole ratio of 20 to 1,000; and (ii) at least two metals which are (a) platinum and (b) at least one other metal selected from the group consisting of titanium, chromium, zinc, gallium, germanium, strontium, yttrium, zirconium, molybdenum, palladium, tin, barium, cerium, tungsten, osmium, lead, cadmium, mercury, indium, lanthanum and beryllium. This catalyst composition is useful particularly for the isomerization of aromatic hydrocarbons and reforming of naphtha.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 307,435 filedOct. 1, 1981, now abandoned, which in turn is a continuation-in-partapplication of application Ser. No. 133,793 filed Mar. 25, 1980 now U.S.Pat. No. 4,331,822.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved catalyst composition. Morespecifically, it pertains to an improved platinum-zeolite type catalystcomposition having a long life, excellent heat resistance and highactivity and selectivity for conversion of aromatic hydrocarbons, forexample the isomerization of xylenes and reforming of naphtha.

2. Description of the Prior Art

Zeolite, or crystalline aluminosilicate, generally has high activity inthe conversion reactions of hydrocarbons, such as cracking,hydrocracking, reforming, isomerization and alkylation. Many catalystscompositions based on zeolite have therefore been proposed to date.Isomerization of xylenes is one typical reaction which is carried out inthe presence of a zeolite-base catalyst.

Isomerization of xylenes is industrially performed by the steps, insuitable combinations, of isomerizing an aromatic hydrocarbon stockcontaining mainly xylene isomers, separating a specified xylene isomer,normally p-xylene, from the resulting isomerization reaction mixture,and recycling the mixture left after the separation. It is industriallysignificant in this case, for an increased efficiency of theisomerization reaction and a reduced cost of production, to adjust thecomposition of the xylene isomers in the isomerization reaction productas closely as possible to the thermodynamic equilibrium composition, andto inhibit side-reactions such as the decomposition of xylenes(particularly, the hydrogenation of the benzene ring) anddisproportionation reaction.

Many methods for isomerizing xylenes have been suggested in the past,and many of them involve the use of a crystalline aluminosilicatezeolite-containing catalyst. Extensive work has been done to improve anddevelop catalysts and improve the isomerization reaction conditions inregard to the aforesaid prior methods, and a number of suggestions havebeen made as a result of such work. In particular, much research effortshave been concentrated on methods involving changing the shape orstructure of the zeolite catalyst itself; methods involving modifyingthe zeolite catalyst by subjecting it to a physical treatment, forexample heat-treatment, and methods involving chemically modifying thezeolite catalyst by adding various ingredients. For example, there havebeen suggested a method in which Y-type zeolite is treated with superheated steam to improve its activity and stability (see U.S. Pat. No.3,887,630), and a method in which MoO₃ is supported on offretite toimprove its activity to decompose ethylbenzene (see U.S. Pat. No.3,848,009).

None of the prior suggested catalysts for isomerization of xylenescompletely meets two contradictory requirements (a) and (b) below. (a)To have superior activity on the isomerization of xylenes, and (b) togreatly reduce undesirable side-reactions (such as the hydrogenation ofthe benzene ring, hydrogenolysis, demethylation, and particularlydisproportionation and transalkylation).

In the case of isomerizing xylene isomers containing ethylbenzene, it isdesirable to deethylate ethylbenzene in addition to the isomerizationreaction of the xylenes, and some methods for this purpose have beensuggested, for example as seen in U.S. Pat. Nos. 4,098,836, 4,163,028,and 4,152,363.

In the previously suggested methods, however, undesirable side-reactionssuch as hydrogenation of the benzene ring, disproportionation of xylenesand transalkylation of xylenes and ethylbenzene take place in additionto the isomerization of xylenes and the deethylation of ethylbenzene,and a loss of xylenes cannot be avoided.

For example, the aforesaid three U.S. Patents disclose a method forisomerizing xylene isomers containing ethylbenzene using ZSM-serieszeolites modified with a metal of Group VIII of the Periodic Table suchas platinum or nickel. With ZSM-series zeolite catalysts modified withnickel (with a nickel content of at least 2% by weight), demethylationof xylene is promoted under severe reaction conditions in which theconversion of ethylbenzene is high, and the loss of xylene increases. Ithas therefore been considered to be advantageous in industrial operationto use a platinum-group metal which induces little demethylation.ZSM-series zeolites modified with platinum have superior activity ofisomerizing xylenes and superior ability to deethylate ethylbenzeneselectively. However, platinum itself has a high ability to hydrogenatethe benzene ring, and the hydrogenation occurs markedly as thetemperature decreases owing to thermodynamic equilibrium. Consequentlythe amount of naphthenes formed increases and a loss of xyleneincreases. Accordingly, ZSM-type zeolite catalysts modified withplatinum need to be used in industrial applications at temperatures ofas high as more than 800° F. (427° C.). The temperature required for theisomerization reaction is affected by the space velocity, but generally,temperatures of about 300° to 340° C. are sufficient. At hightemperatures, the isomerization is not improved, but rather undesirableside-reactions such as disproportionation and transalkylation arepromoted to cause an increased loss of xylenes.

In order to avoid such undesirable reactions as much as possible, amethod has also been suggested in which the space velocity based on thezeolite catalyst is increased to increase the optimum isomerizationtemperature to a level higher than in ordinary methods and therefore topromote deethylation while inhibiting a loss of xylenes attributed todisproportionation, etc. (see U.S. Pat. No. 4,152,363). With thismethod, however, it is difficult to maintain the isomerization at a highlevel, and the degradation of the catalyst increases because thetemperature and the space velocity are high.

SUMMARY OF THE INVENTION

It is a primary object of this invention to provide an improvedplatinum-zeolite catalyst which is significantly free from the defectsof the platinum-containing ZSM-series zeolite catalysts, such as theirability to catalyze the hydrogenation of the benzene ring, thedisproportionation of xylene and the transalkylation reaction of xyleneand ethylbenzene, while retaining their superior ability to isomerizexylenes and to selectively deethylate ethylbenzene.

Other objects and advantages will become apparent from the followingdescription.

According to this invention, there is provided, a catalyst compositioncomprising

(i) a crystalline aluminosilicate selected from the group consisting ofzeolite ZSM-5, zeolite ZSM-11, zeolite ZSM-12, zeolite ZSM-35 and ZSM-38and having a silica/alumina mole ratio of 20 to 1,000, and

(ii) at least two metals which are

(a) platinum, and

(b) at least one other metal selected from the group consisting oftitanium, chromium, zinc, gallium, germanium, strontium, yttrium,zirconium, molybdenum, palladium, tin, barium, cerium, tungsten, osmium,lead, cadmium, mercury, indium, lanthanum and beryllium.

The crystalline aluminosilicate (to be sometimes referred to as zeolite)forming the base of the catalyst of this invention contains mainlyhydrogen or a hydrogen precursor such as an ammonium ion at a cationsite and has a silica/alumina mole ratio of from 20 to 1000, morepreferably from 30 to 200. In other words, a so-called high-silicazeolite having a high content of silica relative to alumina is used as abase of the catalyst. Many zeolites having a high silica contentrelative to alumina have been suggested heretofore, and a zeolite havingan extremely high silica content represented by a silica/alumina moleratio of as high as 2,000 is also known. In the present invention, thereis conveniently used a low zeolite which has a relatively lowsilica/alumina ratio and therefore, has a relatively high acid activityattributed to the alumina component.

Crystalline aluminosilicates, or zeolites, having a silica/alumina moleratio within the above-specified range include ZSM series zeolitesdeveloped by Mobil Oil Corporation. The present invention isparticularly characterized by the fact that zeolites ZSM-5 (see U.S.Pat. No. 3,702,886) ZSM-11 (U.S. Pat. No. 3,709,979), ZSM-12 (see U.S.Pat. No. 3,832,449), ZSM-35 (see U.S. Pat. No. 4,016,245) and ZSM-38(see U.S. Pat. No. 4,046,859) which exhibit especially good isomerizingactivity on aromatic hydrocarbons are used as bases of the catalystcomposition of the invention.

These zeolites are generally available in a form containing an alkalimetal ion or an alkaline earth metal ion at the cation site. In thepresent invention, these zeolites are converted to H-form zeolites, andused in a form containing mainly a hydrogen ion or a hydrogen-precursorion such as an ammonium ion at the cation site. The content of thehydrogen ion or the hydrogen-precursor ion is not strictly limited. Itis very desirable that generally at least 50%, preferably at least 75%,of the entire cation sites present in the zeolite be occupied by thehydrogen ion or hydrogen-precursor ion. Accordingly, unless otherwiseindicated, "zeolite" used in the present application denotes H-formzeolite.

It has been found that the use of ZSM-5 zeolite as a base of catalystproduces the best effect. Thus, according to the most preferredembodiment of this invention, ZSM-5 zeolite is used as a base of thecatalyst composition.

According to this invention, there is used as a main ingredient of thecatalyst composition a product obtained by modifying the aforesaidzeolite with at least two metals which are (a) platinum [to be referredto as metal (a)], and (b) at least one metal selected from the groupconsisting of titanium, chromium, zinc, gallium, germanium, strontium,yttrium, zirconium, molybdenum, palladium, tin, barium, cerium,tungsten, osmium, lead, cadmium, mercury, indium, lanthanum andberyllium [to be referred to as metal (b)].

Investigations of the present inventors have led to the surprisingdiscovery that zeolite catalysts modified with only platinum havesuperior ability to isomerize xylenes but at the same time, catalyzeundesirable reactions such as the hydrogenation of the benzene ring andthe demethylation of xylenes and these catalytic reactions cause anincreased loss of xylenes in the isomerization of xylenes, but that whenboth platinum [metal (a)] and metal (b) are incorporated together intozeolite, the resulting catalyst retains the high ability to isomerizexylenes which the zeolite having only metal (a) incorporated thereinpossesses, and its undesirable catalytic reaction on such reactions asthe hydrogenation of the benzene ring and the demethylation of xylenescan be effectively inhibited.

Titanium, tin, barium, indium and lanthanum are preferred as metal (b)because they have the great ability to inhibit the side-reactions.Titanium and tin are most preferred.

The term "modified with the metal (a) and (b)", as used herein, meansthat the metals (a) and (b) are ion-exchanged at the cation site ofzeolite and/or the metals (a) and (b) or compounds containing them arephysically deposited on the surface of zeolite.

Zeolites modified with metals (a) and (b) may be prepared by methodsgenerally known in the modification of zeolites with metals.Modification with metal (a) and modifications with metal (b) may beperformed separately in the desired order, or simultaneously. In apreferred embodiment, modification with metal (b) is carried out afterthe modification with metal (a).

To facilitate understanding, typical examples of the modifying methodare described below in detail.

Commercially available zeolites generally have alkali metal ions oralkaline earth metal ions such as Na, K or Ca substituted at the cationsite thereof. Hence, the alkali metal or alkaline earth metal ion isexchanged with hydrogen or an ammonium ion. This exchange may beperformed simultaneously with, or prior to, the modification with metal(a).

One method comprises dipping a zeolite having its cation sitesubstituted with an alkali metal or alkaline earth metal ion in anaqueous solution containing a metal (a) ion and an ammonium ion to givea zeolite product which is modified with the metal (a) and in which agreater portion of the cation site is of the ammonium ion form.Calcination of the resulting ammonium ion-form zeolite modified with themetal (a) at a temperature of about 200° to 600° C. gives a hydrogenion-form zeolite modified with the metal (a).

Another method comprises treating a zeolite having its cation sitesubstituted with an alkali metal or alkaline earth metal ion with aninorganic or organic acid such as hydrochloric acid, sulfuric acid,nitric acid, acetic acid or oxalic acid to convert a greater portion ofthe cation site to a hydrogen ion form, and exchanging the hydrogen ionwith a metal (a) ion or depositing the metal (a) on the resultingzeolite.

Still another method comprises treating a zeolite having its cation sidesubstituted by an alkali metal or alkaline earth metal ion with anaqueous solution of a water-soluble ammonium compound to form a zeolitehaving a greater portion of its cation site substituted with an ammoniumion, which zeolite is then optionally converted to an H-form zeolite bycalcination at a temperature of, for example, about 200° to about 600°C., and finally exchanging the ammonium ion or hydrogen ion with a metal(a) ion, or depositing the metal (a) on the ammonium ion-type orhydrogen ion-type zeolite. In this method, substitution by an ammoniumion can be easily carried out by contacting the zeolite with an aqueoussolution of a water-soluble ammonium compound such as ammonium chlorideor ammonium nitrate in a concentration of 5 to 20% by weight.

Ion exchange of zeolite with a metal (a) and/or deposition of the metal(a) on the zeolite can be performed by techniques known to be used insubjecting ordinary zeolites to ion exchange with metal (a) or indepositing noble metal (a) on such zeolites.

For example, a zeolite to be treated is contacted with an aqueous ornon-aqueous medium containing a compound of the desired noble metaldissolved therein. Such noble metal compounds include the halides,oxides, sulfides, oxy acid salts, and complexes. When zeolite ismodified with metal (a) (platinum), the zeolite may be impregnated withan aqueous solution of a water-soluble platinum compound (such as H₂PtCl₆, or PtCl₂) and then water is evaporated off to deposit platinum onthe zeolite. Or the zeolite may be dipped in an aqueous solution of aplatinum compound having ion exchange ability such as a platinum-aminecomplex [e.g., Pt(NH₃)₄ Cl₂ ], and then subjected to filtration,followed by sufficient washing. As a result, the zeolite ision-exchanged with a platinum cation.

Prior to the modification treatment with metal (a), zeolite may beheated for 1 to 50 hours in an oxygen atmosphere such as air or an inertgaseous atmosphere such as nitrogen at a temperature of 100° to 700° C.,preferably 200° to 600° C. This generally gives better catalysts.

The zeolite modified with metal (a) may be heated in anoxygen-containing atmosphere such as air or an inert gaseous atmospheresuch as nitrogen at a temperature of 100° to 700° C., preferably 200° to600° C., for about 1 to about 5 hours. This heat-treatment is preferredin this invention.

The zeolite modified with metal (a) in the above manner is then modifiedwith metal (b). Modification with metal (b) may be carried out by thesame method and under the same conditions as in the modification withmetal (a) described hereinabove. Accordingly, the modification withmetal (b) is not particularly different from usually known methods forpreparing modified zeolites using various methods.

Examples of the various metal compounds used to perform modificationwith metal (b) are given below. These examples are merely illustrative,and it should be understood that any water-soluble or solvent-solublecompounds of the respective metals can be equally used even if they arenot specifically exemplified herein.

(1) Titanium Compounds

Titanium fluoride, chloride, bromide, iodide sulfate and nitrate,ammonium hexafluorotitanate, ammonium pentafluoroperoxotitanate,ammonium hexachlorotitanate, diethyl ammonium hexachlorotitanate andhexabromotitanate, and bis(acetonitrile)tetrachlorotitanium.

(2) Chromium Compounds

Chromous chloride, chromous sulfate, chromous acetate, chromic chloride,chromic nitrate, chromic sulfate, hexamine chromic compound, dichromicacid, and ammonium dichromate.

(3) Germanium Compounds

Germanium tetrachloride, germanium dichloride, and germanium tetraalkyl.

(4) Molybdenum compounds

Molybdic acid, ammonium molybdate, and molybdenum pentachloride.

(5) Palladium Compounds

Palladium chloride, palladium sulfate, palladium nitrate, andtetraammine palladium chloride.

(6) Tin Compounds

Stannous chloride, tin tetrachloride, chlorostannous acid, tintetraalkyl, ammonium hexachlorostannate, and tetraethylammoniumtrichlorostannate.

(7) Barium Compounds

Barium fluoride, chloride, chlorate perchlorate, bromide, bromate,iodide, thiosulfate, dithionate, sulfate, nitrate, phosphate, carbonate,thiocyanate, metalsilicate, acetate, hydroxide, formate,hydrogen-phosphate, lactate, oxalate, nitrite and sulfite.

(10) Tungsten Compounds

Tungstic acid, and ammonium paratungstate.

(11) Osmium Compounds

Osmic acid, and osmium tetrachloride.

(12) Lead Compounds

Lead acetate, lead nitrate, lead chlorate, and lead tetraalkyl.

(13) Cadmium Compounds

Cadmium chloride, perchlorate, bromide, iodide, sulfate, nitrate,cyanide, thiocyanate, carbonate, formate, hydroxide and sulfide,tris(ethylenediamine) cadmium nitrate, anddichloro(ethylenediamine)cadmium.

(14) Indium Compounds

Indium fluoride, chloride, bromide, iodide, perchlorate, sulfate andnitrate, ammonium hexafluoroindate, and ammonium aquapentachloroindate.

(15) Other Metal Compounds

Compounds of strontium, beryllium, gallium, yttrium, zirconium, zinc,cerium, lanthanum, and mercury, such as the corresponding fluorides,chlorides, bromides, iodides, perchlorates, cyanides, sulfates,nitrates, nitrites, sulfides, acetates, oxalates, formates, lactates,citrates, carbonates, phosphates, thiocyanates, thiosulfates,hydroxides, oxides, chlorates, chlorites, iodate, and various kinds ofcomplex compounds thereof.

The contents of the metals (a) and (b) in the zeolite modified with themetals (a) and (b) in accordance with this invention can be varieddepending upon the type of the metal used. The content of metal (a) isgenerally 0.001 to 2% by weight, preferably 0.005 to 1.5% by weight,more preferably 0.01 to 1% by weight, based on the weight of thecrystalline aluminosilicate. The contents of the metal (b) is such thatthe atomic ratio of metal (a) to metal (b) is generally from 1:0.01 to1:10, preferably from 1:0.5 to 1:5, more preferably from 1:0.1 to 1:3.

The catalyst of this invention so prepared contains the metal (a) in theform of a cation and/or oxide and the metal (b) in the form of a cationand/or oxide depending upon the type of the metal, before it is reducedprior to use in the reaction. When the catalyst is reduced prior to usein the reaction, the metal (a) is converted to an elemental form, andthe metal (b), to an element, oxide or cataion, or mixtures thereof.

The zeolite catalyst of the invention can be prepared either as a finepowder or an various other desired shapes such as pellets or tabletsmolded in a customary manner. A shaped article of the modified zeolitecan be obtained in a customary manner by mixing the modified zeolitewith a synthetic or natural refractory inorganic oxide usually employedas a binder for zeolite-type catalysts, such as silica, alumina,silica-alumina, kaolin or silica-magnesia, shaping the mixture into thedesired configuration, and then calcining the shaped article.Advantageously, the amount of the modified zeolite as an active catalystingredient in the shaped article is generally 1 to 99% by weight,preferably 10 to 90% by weight, based on the weight of the shapedarticle.

In use, the catalyst composed of zeolite modified with the metals (a)and (b) prepared in the above-mentioned manner is treated in a reducingatmosphere such as a hydrogen gas at a temperature of 200° to 600° C.,preferably 250° to 550° C. This reducing treatment is usually carriedout after the catalyst has been filled in a reactor.

The catalyst composition of this invention prepared in the above mannercan be characterized by various excellent properties described below.

(1) Cyclohexane/n-hexane sorption ratio

The cyclohexane/n-hexane sorption ratio is a parameter which representsa measure of the pore dimension of the zeolite catalyst, and denotes theratio of the weight of cyclohexane adsorbed per unit weight of thezeolite catalyst at a constant temperature and pressure to the weight ofn-hexane adsorbed per unit weight of the zeolite catalyst at theconstant temperature and pressure. That this ratio is low means thatmolecules having a large cross section such as cyclohexane, havedifficulty in diffusing through the pores of the zeolite. This bringsabout an advantage of increasing selectivity in a catalyzed reaction.The amount of cyclohexane or n-hexane adsorbed per unit weight of thezeolite can be measured by weighing a fixed amount of the zeolitecatalyst calcined at 450° C. for 8 hours in an electric furnace, thenmaintaining the weighed zeolite for 6 hours in an atmosphere of asaturated gas of cyclohexane or n-hexane at 25° C. and 120±20 mmHg,further weighing the zeolite catalyst after it has been maintained at25° C. and 120±20 mmHg in the absence of cyclohexane or n-hexane, andcalculating the weight difference of the catalyst before and afteradsorption. A more specific method of measurement is described in detailin Example 3 given hereinbelow.

The catalyst zeolite provided by this invention generally has acyclohexane/n-hexane sorption ratio of not more than 0.95, preferablynot more than 0.8, more preferably not more than 0.6. The lower limit tothe sorption ratio varies depending upon the type of the startingzeolite used in the preparation of the catalyst and the types andamounts of the metal (a) and/or the metal (b) used in the catalystpreparation. Generally, it is about 0.05, desirably 0.1 or more.

(2) Activity Index

The "activity index", as used in the present application, denotes therelative cracking activity of the catalyst composition of the inventionin comparison with a conventional highly active silica-alumina crackingcatalyst. It is measured by the following method.

A catalyst sample molded to a size of 10-20 mesh is calcined in air at450° C. for 8 hours. 1.5 ml of the calcined catalyst is packed into aquartz reactor tube. Nitrogen gas saturated with n-hexane at 25° C. isfed into the catalyst bed kept at constant temperature (200° C.) at arate of 10 ml/min at atmospheric pressure. The conversion of n-hexane ismeasured, and the reaction rate constant at that temperature iscalculated. The activity index (A.I.) is computed from the followingequation. ##EQU1##

The method for measuring A.I. is described in detail in Example 2 givenhereinbelow.

The catalyst zeolite of the invention generally has an A.I. of not lessthan 100, preferably not less than 1,000, when it is measured by theabove method.

(3) Hydrogenation Index

The term "hydrogenation index" (to be abbreviated H.I.), used in thepresent application, denotes the total weight percent of C₆ naphtheneswhich are formed when a 1:1 (mole) gaseous mixture of benzene andhydrogen is passed over the zeolite catalyst of the invention underfixed reaction conditions (200° C., 1 atm.) at a weight hourly spacevelocity (WSHV) of 8 hr⁻¹. That the H.I. is high means that the catalysthas high hydrogenating activity on the benzene ring. The high H.I. leadsto an increase in the loss of aromatic hydrocarbons in the reactions.

H.I. is measured by the following method.

A sample zeolite catalyst molded into pellets having a size of 10 to 20mesh is calcined at 450° C. for 8 hours in an electric furnace, and afixed amount of the calcined catalyst sample is weighed. It is thenpacked into a fixed bed reactor vessel. A 1:1 (mole) mixture of benzeneand hydrogen is fed into the catalyst bed under fixed reactionconditions (200° C., 1 atm.) at a WHSV of 8 hr⁻¹. After a lapse of twohours from the initiation of feeding, the total amount (weight percent)of C₆ naphthenes is measured, and defined as H.I.

The catalyst composition of this invention generally has an H.I. of notmore than 6%, preferably not more than 2%, more preferably not more than0.5% when it is measured by the above method. One advantage of theinvention is that when the catalyst composition of the invention is usedin the isomerization of xylene, the loss of xylenes is very small.

(4) Catalyst life

Since the catalyst composition of the invention has a very low H.I.value as stated above, hydrogenation and hydrogenolysis of the benzenering do not appreciably take place. This offers the advantage thatdeposition of coke on the catalyst surface is very much reduced.Accordingly, the catalyst of the invention permits operation for alonger period of time than conventional catalysts, and enables thereaction to be carried out at lower temperatures and pressures.

(5) Heat stability

Since deposition of coke on the surface of the catalyst composition ofthis invention is reduced as stated above, heat generation during theregeneration of the catalyst is small, and therefore, the platinum sitedoes not easily undergo damage during the regeneration. Then, after theoperation the performance of the catalyst composition is stable.

Thus, the catalyst composition provided by this invention can be used,for example, as in isomerization catalyst in isomerizing an aromatichydrocarbon stock containing predominantly xylene isomers not attaininga thermodynamic equilibrium composition at an elevated temperature inthe vapor phase in the presence of hydrogen.

The aromatic hydrocarbon stock to be used in the isomerization ofxylenes prodominantly contains xylene isomers which has not attained athermodynamic equilibrium composition. As is well known, xylene containsthree isomers, ortho-, meta- and para-isomers. It is known that when amixture in an arbitrary ratio of the three isomers is subjected to anisomerization reaction, the reaction reaches an equilibrium when theratio among the three isomers attains a certain specific value, andapparently no further advance of the isomerization is noted. Thecomposition of the xylene isomers at such an equilibrium state is calledthe "thermodynamic equilibrium composition". The thermodynamicequilibrium composition varies slightly depending upon temperature, andfor example, the xylene isomers have the following thermodynamicequilibrium composition at the following temperature.

    ______________________________________                                        [I] Mixture consisting only of three xylene isomers                           (at 427° C.):-                                                         p-Xylene        23.4% by weight                                               m-xylene        52.1% by weight                                               o-Xylene        24.5% by weight                                               [II] Mixture of xylene isomers and ethylbenzene                               (at 427° C.):-                                                         Ethylbenzene    8.3% by weight                                                p-Xylene        21.5% by weight                                               m-Xylene        47.8% by weight                                               o-Xylene        22.4% by weight                                                               100% by weight                                                                             in total                                         ______________________________________                                    

In the present specification, the term "xylene isomeric mixture notattaining a thermodynamic equilibrium composition" denotes a xyleneisomers mixture in which the concentration of at least one of the threexylene isomers falls outside the thermodynamic equilibrium composition.

The aromatic hydrocarbon stock to be used as a starting material in theprocess of this invention may consist only of the xylene isomers, or maybe a mixture of the xylene isomers with another aromatic hydrocarbonsuch as ethylbenzene, benzene, toluene, ethyltoluene, trimethylbenzene,diethylbenzene, ethylxylene, and tetramethylbenzene. In the latter case,the xylene isomeric mixture is present desirably in an amount ofgenerally at least 30% by weight, preferably at least 50% by weight,based on the weight of the aromatic hydrocarbon stock.

C₈ aromatic hydrocarbon fractions obtained by reforming, thermalcracking or hydrocracking of naphtha can be used especiallyadvantageously as the aromatic hydrocarbon stock. These fractionscontain ethylbenzene of the same number of carbons in addition to thexylene isomers. Very good results can be obtained in this catalystcomposition when using a C₈ -aromatic hydrocarbon fraction whichcontains the xylene isomers and ethylbenzene in a total amount of atleast 80%, preferably at least 90% by weight, based on the weight of thefraction.

Isomerization of the aromatic hydrocarbon stock can be performed underknown reaction conditions except that the above-specified catalyst isused. The reaction temperature is generally 250° to 450° C., preferably270° to 400° C., especially preferably 280° to 380° C., and the partialpressure of hydrogen is generally 0 to 25 kg/cm².G, preferably 0 to 20kg/cm².G, especially preferably 0 to 12 kg/cm².G.

In practice, the starting aromatic hydrocarbon stock is fed at a ratewhich can be varied widely according to the type of the hydrocarbonstock used, the type of the catalyst, etc. It is generally advantageousto feed the hydrocarbon stock at a weight hourly space velocity of about1 to about 500, preferably 2 to 100, more preferably 3 to 50.

Not only can the catalyst composition of the invention be usedadvantageously in the isomerization reaction of xylenes, but also it canbe utilized in the transalkylation and dealkylation (particularlyselective dealkylation of an alkyl group having at least 2 carbon atoms)of alkyl aromatic hydrocarbons and the alkylation of aromatichydrocarbons.

The catalyst composition of this invention also becomes an excellentcatalyst having high activity and a long active lifetime in thereforming of naphtha involving dehydrogenation of naphthenes,isomerization and cracking of n-paraffins, and dehydrogenation andcyclization of paraffins.

In the present specification and appended claims, the "weight hourlyspace velocity" is a value calculated in accordance with the followingequation. ##EQU2## The "weight of the catalyst", as used herein, denotesthe weight of crystalline aluminosilicate which forms the base of thecatalyst.

The isomerization reaction is carried out in the presence of hydrogen.The rate of feeding hydrogen in this case can be varied widely accordingto the type of the aromatic hydrocarbon material and/or the catalyst,etc. Generally, it is appropriate to feed hydrogen at such a rate thatthe hydrogen/hydrocarbon mole ratio is generally from 0.1 to 15,preferably 1 to 10, more preferably from 1 to 8.

The catalyst composition of this invention brings about the followingexcellent technical advantages over similar conventional techniques, andcan contribute greatly to industry.

(1) Since the hydrogenation and the demethylation of xylene can bemarkedly inhibited, a loss of xylene is decreased drastically, and theisomerization yield of xylene increases.

(2) Since the process can be operated under an elevated hydrogen partialpressure, the efficiency of the xylene manufacturing facilities can begreatly increased.

(3) Coke formation on a catalyst can be inhibited, and the operatingefficiency of the apparatus can be improved greatly.

The following Examples illustrate the present invention in greaterdetail.

EXAMPLE 1 (a) Preparation of H-ZSM-5

Zeolite ZSM-5 was synthesized in accordance with the method disclosed inthe specification of U.S. Pat. No. 3,965,207. In the synthesis,n-tripropylamine and n-propyl bromide were added as a source of anorganic nitrogen cation. The synthesized product was identified as ZSM-5from its X-ray diffraction pattern. The resulting ZSM-5 was filtered,and fully washed with water. It was dried in a drying oven at 100° C.for 8 hours, and then at 200° C. for 16 hours, and then calcined in anelectric muffle furnace under an air stream at 450° C. for 16 hours.Then, 250 g of the calcined product was subjected to ion-exchange at 80°C. for 24 hours using 1.5 liters of a 5% by weight aqueous solution ofammonium chloride. Further this procedure was repeated two times. Then,the product was thoroughly washed with water, dried in a drying oven at100° C. for 8 hours and 200° C. for 16 hours, and in an electric mufflefurnace under a stream of air at 450° C. for 16 hours to obtain H³⁰-form zeolite ZSM-5 which contained 0.05% by weight of sodium and had asilica/alumina mole ratio of 92.

(b) Preparation of Pt/ZSM-5

0.173 g of [Pt(NH₃)₄ ]Cl₂ was dissolved in 90 cc of water, and 30 g ofthe H⁺ -form ZSM-5 obtained by the method shown in (a) above was added.With occasional shaking, the zeolite was immersed therein at 50° C. for8 hours, then filtered, washed fully with water at room temperature, anddried in an drying oven at 100° C. for 8 hours and then at 200° C. for16 hours. It was calcined in an electric muffle furnace under a streamof air at 450° C. for 3 hours to afford Pt/ZSM-5 which contained 0.24%,based on the total weight of the catalyst, of platinum (this catalyst isreferred to as catalyst A).

(c) Preparation of Pt/ZSM-5

120 ml of 2.5% aqueous ammonia was added to 22.0 g of H-ZSM-5, and whilethey were sufficiently stirred with a glass rod, a solution of 0.113 gof [Pt(NH₃)₄ ]Cl₂ in 60 ml of a 2.5% aqueous ammonia was added dropwiseby a pipette. The mixture was stirred at room temperature for 5 hoursusing a magnetic stirrer, and then washed with deionized water until theelectric conductivity of the filtrate became not more than 15 μv/cm. Theproduct was then dried at 100° C. and 200° C. both for 4 hours, andcalcined in an electric muffle furnace under a stream of air for 4hours. The platinum content of the product was 0.28% by weight. Theproduct is referred to as catalyst B. By a similar operation, catalyst Cto H having the platinum contents shown in Table 1 were prepared.

(d) Pt-ZSM-5 with various metals supported thereon

Each of the various metal salts shown in Table 1 was weighed so that theatomic ratio of the metal to platinum reached the prescribed valuesshown in Table 1, and dissolved in a suitable solvent (deionized waterunless otherwise specified). To the solution was added Pt-ZSM-5 preparedas above, and the mixture was evaporated to dryness to impregnate themetal salt therein. The product was dried at 100° C. and then at 200°C., and calcined in an electric muffle furnace under a stream of air at450° C. to prepare powders of Pt-ZSM-5 having various metals supportedthereon.

As a specific example, Pt-ZSM-5 having indium supported thereon wasprepared as follows:

13.5 mg of InCl₃.4H₂ O (the atomic ratio of indium to platinumcorresponded to 1.2) was dissolved in 50 ml of deionized water, and 3 gof catalyst E was added. In a constant temperature bath at 70° C., themixture was heated for 4 hours with occasional shaking. Then, using arotary evaporator, water was distilled off at a temperature of 45° C.The solid residue was dried in a drying oven at 100° C. and 200° C. bothfor 4 hours, and calcined in an electric muffle furnace under a streamof nitrogen at 450° C. for 4 hours to afford a catalyst E-1.

                                      TABLE 1                                     __________________________________________________________________________         Concentration  Atomic                                                    Catalyst                                                                           of platinum    ratio of                                                  series                                                                             (wt. %, based  metal (b)                                                 No.  on zeolite)                                                                           Metal (b)                                                                            to Pt                                                                              Salt of metal (b)                                                                        Solvent                                   __________________________________________________________________________    A    0.24    --     --   --         --                                        A-1  "       Germanium                                                                            0.9  GeCl.sub.4 Isopropyl alcohol                         A-2  "       Tin    0.5  SnCl.sub.2.2H.sub. 2 O                                                                   HCl/water                                 A-3  "       Lead   0.3  Pb(NO.sub.3).sub.2                                                                       Water                                     A-4  "       Chromium                                                                             1.3  Cr(NO.sub.3).sub.3.9H.sub. 2 O                                                           "                                         A-5  "       Molybdenum                                                                           0.7  (NH.sub.4).sub.6 Mo.sub.7 O.sub.27.4H.sub. 2                                             "                                         A-6  "       Tungsten                                                                             0.4  (NH.sub.4).sub.10 W.sub.12 O.sub.41.5H.sub. 2                                            "                                         A-7  "       Osmium 0.3  OsO.sub.4  "                                         A-8  "       Palladium                                                                            0.6  Pd(NH.sub.3).sub.4 Cl.sub.2                                                              "                                         B    0.27    --     --   --         --                                        B-1  "       Strontium                                                                            0.5  Sr(ClO.sub.4).sub.2.2H.sub. 2 O                                                          Water                                     B-2  "       Beryllium                                                                            0.5  Be(NO.sub.3).sub.2.3H.sub. 2 O                                                           "                                         B-3  "       Gallium                                                                              0.5  Ga(NO.sub.3).sub.2.8H.sub. 2 O                                                           "                                         B-4  "       Cerium 0.5  Ce(NO.sub.3).sub.3.6H.sub. 2 O                                                           "                                         B-5  "       Barium 0.2  Ba(NO.sub.2).sub.2.H.sub. 2 O                                                            "                                         C    0.28    --     --   --         --                                        C-1  "       Yttrium                                                                              1.1  Y(NO.sub.3).sub.3.6H.sub. 2 O                                                            Water                                     C-2  "       Zirconium                                                                            0.5  Zr(NO.sub.3).sub.2.2H.sub. 2 O                                                           "                                         D    0.27    --     --   --         --                                        D-1  "       Zinc   1.1  Zn(NO.sub.3).sub.2.6H.sub. 2 O                                                           Water                                     D-2  "       Titanium                                                                             0.5  Ti(SO.sub.4).sub.2                                                                       "                                         E    0.26    --     --   --         --                                        E-1  "       Indium 1.2  InCl.sub.3.4H.sub. 2 O                                                                   Water                                     E-2  "       Lanthanum                                                                            1.2  La(NO.sub.3).sub.3.6H.sub. 2 O                                                           "                                         F    0.27    --     --   --         --                                        F-1  "       Cadmium                                                                              1.1  CdCl.sub.2.21/2 H.sub.2 O                                                                Water                                     G    0.25    --     --   --         --                                        G-1  "       Mercury                                                                              1.2  Hg(NO.sub.3).sub.2.H.sub. 2 O                                                            Water                                     H-1  0.5     Tin    0.3  SnCl.sub.2.2H.sub. 2 O                                                                   HCl/Water                                 H-2  "       Tin    3.3  SnCl.sub.2.2H.sub. 2 O                                                                   "                                         __________________________________________________________________________

EXAMPLE 2

The powdery catalysts HZSM-5, Pt/ZSM-5 and bimetallic ZSM-5 obtained inExample 1 were each molded into a size of 10 to 20 mesh. Each of themolded articles was calcined in an electric muffle furnace in air at450° C. for 8 hours, and then 1.5 ml of the calcined molded catalyst waspacked into a Pyrex glass tube reactor. Nitrogen gas was passed throughn-hexane at 25° C. in an gas absorbing bottle, and the saturated gaseousstream (the partial pressure of hexane was 0.2 atm.) was fed into thecatalyst bed at a rate of 10 ml/min. The reaction temperature wasadjusted such that the conversion of n-hexane was maintained at 5 to40%. The above conversion could be achieved at a reaction temperature of150° to 250° C.

The conversion of n-hexane is defined as follows: ##EQU3##

The product formed during a time period between 20 minutes and 30minutes after the start of feeding was sampled, and analyzed by gaschromatography.

The reaction velocity constant at each reaction temperature wascalculated as follows. ##EQU4## wherein k (sec⁻¹) is the rate constant,τ (sec) is the volume (ml) of the catalyst/the flow rate (ml/sec) of thefeed gas, and ε is the conversion of n-hexane.

The reaction rate constant of the catalyst at 200° C. can be determinedfrom the Arrhenius' plot.

As a standard silica-alumina catalyst, N-631-HN (product of NikkiChenicals Ltd.) was used, and its reaction rate constant was calculatedby the same procedure as above. An n-hexane conversion of 5 to 40% wasobtained at a temperature of 400° to 500° C. The reaction velocityconstant of the standard catalyst at 200° C. was calculated by anextrapolation method using the activation energy obtained within theabove-mentioned temperature range.

The ratio of the reaction rate constant of the catalyst to that of thestandard catalyst at 200° C. is defined as the activity index (A.I.).The A.I. values of H-ZSM-5 and A-G series catalysts are summarized inTable 2.

It is seen from Table 2 that the ZSM-5 containing Pt (a) and the metal(b) has sufficient catalytic activity.

                  TABLE 2                                                         ______________________________________                                        Catalyst   Metal (b)         A.I.                                             ______________________________________                                        H--ZSM-5   --                16,000                                           A          --                11,000                                           A-1        Ge                8,800                                            A-2        Sn                8,700                                            A-3        Pb                7,700                                            A-4        Cr                7,500                                            A-5        Mo                7,900                                            A-6        W                 9,900                                            A-7        Os                9,500                                            A-8        Pd                9,900                                            B          --                11,000                                           B-1        Sr                7,700                                            B-2        Be                8,700                                            B-3        Ga                7,900                                            B-4        Ce                10,000                                           B-5        Ba                4,800                                            C          --                11,000                                           C-1        Y                 9,500                                            C-2        Zr                10,000                                           D          --                11,000                                           D-1        Zn                7,100                                            D-2        Ti                3,400                                            E          --                11,000                                           E-1        In                9,700                                            E-2        La                8,800                                            F          --                11,000                                           F-1        Cd                6,000                                            G          --                11,000                                           G-1        Hg                4,100                                            ______________________________________                                    

EXAMPLE 3

To remove the adhering water, the powdery H-ZSM-5, Pt/ZSM-5 andbimetallic ZSM-5 catalysts obtained in Example 1 were each calcined inan electrical muffle furnace in air at 450° C. for 8 hours. About 1 g ofeach of the calcined catalysts was weighed into a weighing bottle. Theweighed zeolite was then allowed to stand in a desiccator containing anadsorbent solvent for 6 hours at 25° C. and 120±20 mmHg to allowadsorption to saturation. Then, the solvent was removed from thedesiccator, and the zeolite was evacuated at 25° C. and 120±20 mmHg for2 hours. The zeolite was again weighed. The amount of the materialadsorbed to zeolite is calculated from the following equation. ##EQU5##wherein v is the amount of the material adsorbed per unit weight of thezeolite, and W₁ and W₂ are the weights of the zeolite before and afteradsorption, respectively.

By the above method, the n-hexane/cyclohexane sorption rate wascalculated, and the results are shown in Table 3.

It is seen from Table 3 that the ZSM-5 containing Pt (a) and the metal(b) has favorable adsorption selectivity. This brings about theimportant advantage that its selectivity for a catalytic reaction isincreased.

                  TABLE 3                                                         ______________________________________                                         Catalyst  Metal (b)                                                                              ##STR1##                                                  ______________________________________                                        H--ZSM-5  --       0.60                                                       A         --       0.46                                                       A-1       Ge       0.44                                                       A-2       Sn       0.40                                                       A-3       Pb       0.42                                                       A-4       Cr       0.45                                                       A-5       Mo       0.49                                                       A-6       W        0.35                                                       A-7       Os       0.41                                                       A-8       Pd       0.40                                                       B         --       0.46                                                       B-1       Sr       0.37                                                       B-2       Be       0.51                                                       B-3       Ga       0.46                                                       B-4       Ce       0.37                                                       B-5       Ba       0.45                                                       C         --       0.46                                                       C-1       Y        0.44                                                       C-2       Zr       0.37                                                       D         --       0.46                                                       D-1       Zn       0.48                                                       D-2       Ti       0.46                                                       E         --       0.46                                                       E-1       In       0.49                                                       E-2       La       0.44                                                       F         --       0.46                                                       F-1       Cd       0.47                                                       G         --       0.46                                                       G-1       Hg       0.44                                                       ______________________________________                                    

EXAMPLE 4

Each of the powdery catalysts Pt/ZSM-5 and bimetallic ZSM-5 obtained inExample 1 was mixed fully with chromatographic alumina gel (300 mesh) ina weight ratio of 1:1, and the mixture was then molded to a size of 10to 20 mesh. The molded article was calcined in an electrical mufflefurnace in air at 450° C. for 8 hours. About 4 g of the molded article,and packed into a fixed bed reactor. The calcined catalyst was thenreduced in hydrogen gas at 400° C. for 2 hours, and then benzene was fedat a rate of 16 g/hour together with hydrogen gas. The reactionconditions were as follows:

Reaction temperature: 200° C.

WHSV: 8.0 hr⁻¹ (based on the weight of the zeolite)

Hydrogen/benzene mole ratio: 1:1

Pressure: atmospheric pressure

Purity of benzene: 99.98%

After a lapse of two hours from the initiation of feeding, the productwas sampled and analyzed by gas chromatography. The total weight percentof C₆ naphthenes was measured, and defined as H.I.

Table 4 summarizes the hydrogenation index (H.I.) of A-H seriescatalysts.

It is seen from Table 4 that the metal (b) markedly reduces thehydrogenating activity of the catalyst on the benzene ring.

                  TABLE 4                                                         ______________________________________                                        Catalyst        Metal (b)                                                                              H. I.                                                ______________________________________                                        A               --       10.90                                                A-1             Ge       1.98                                                 A-2             Sn       0.45                                                 A-3             Pb       4.89                                                 A-4             Cr       2.59                                                 A-5             Mo       2.88                                                 A-6             W        5.23                                                 A-7             Os       4.09                                                 A-8             Pd       4.04                                                 B               --       7.92                                                 B-1             Sr       2.80                                                 B-2             Be       4.26                                                 B-3             Ga       2.20                                                 B-4             Ce       4.40                                                 B-5             Ba       0.35                                                 C               --       1.05                                                 C-1             Y        0.74                                                 C-2             Zr       0.65                                                 D               --       3.37                                                 D-1             Zn       2.46                                                 D-2             Ti       0.24                                                 E               --       4.86                                                 E-1             In       0.11                                                 E-2             La       1.46                                                 F               --       5.90                                                 F-1             Cd       0.05                                                 G               --       5.55                                                 G-1             Hg       0.79                                                 ______________________________________                                    

EXAMPLE 5

Chromatographic alumina gel (300 mesh) was added to each of the powderycatalysts A and A-2 obtained in Example 1 in a weight ratio of 1:1. Theywere well mixed and molded into a size of 10 to 20 mesh. Each of themolded products was calcined in an electric muffle furnace under astream of air at 450° C. for 8 hours, and filled in a fixed bed reactor.Then, each of the molded catalysts was reduced in a stream of hydrogenat 400° C. for 2 hours, and subsequently, a xylene isomeric mixturehaving the composition shown in Table 2 was fed to the reactor.

The reaction conditions were as follows:

Temperature: 350° C.

Weight hourly space velocity (WHSV): 8.0 hr⁻¹ (based on the weight ofzeolite)

Hydrogen/aromatic hydrocarbon mole ratio: 3:1

Pressure: 7.4 kg/cm².G

The composition of the product after a lapse of 50 hours from theinitiation of feeding was as shown in Table 5.

It is seen from the results obtained that when tin is added as the metal(b) to Pt/ZSM-5, the approach to equilibrium of PX, which shows thedegree of isomerization activity, does not at all decrease, and thatwhile the degree of deethylation inherent to platinum is maintained at ahigh level, the inherent ability of platinum to hydrogenate the benzenering and demethylate the xylenes can be drastically inhibited. Thus, aloss of xylene can be greatly decreased.

                  TABLE 5                                                         ______________________________________                                                         Product                                                                       Catalyst A-2                                                                           Catalyst A                                                           (Pt/Sn)  Pt                                                  ______________________________________                                        Composition (wt. %)                                                                        Feed stock                                                       C.sub.2 -C.sub.4     --      1.38     2.54                                                  (*)                                                             C.sub.5 -C.sub.9     0.02    0.12     5.52                                    Benzene      --        4.11       5.10                                        Toluene      2.01      3.08       5.12                                        Ethylbenzene 14.85     8.22       5.79                                        p-Xylene     9.18      19.49      17.62                                       m-Xylene     56.45     44.49      40.22                                       o-Xylene     17.44     17.76      16.05                                       C.sub.9 aromatics                                                                          0.05      0.70       1.71                                        C.sub.10.sup.+ aromatics                                                                   --        0.22       0.33                                        PX approach to     101.0      101.1                                           equilirium (%)                                                                FB composition ratio (%)                                                                         44.6       61.0                                            Xylene loss (%)    1.54       11.0                                            E.sub.B decomposition ratio/                                                                     29.0       5.5                                             xylene loss                                                                   Deethylation ratio (%)                                                                           79.0       88.5                                            Amount of demethylaction                                                                         6.63       19.55                                           (mmole)                                                                       Amount of C.sub.6.sup.+ naphthenes                                                               0.06       4.24                                            formed (wt. %)                                                                C.sub.6 naphthenes/benzene (wt. %)                                                               0.20       14.01                                           ______________________________________                                         NA: nonaromatics composed mainly of paraffins and naphthenes.            

The various items given in the above and subsequent tables are definedas follows: ##EQU6##

The various abbreviations given above mean the following.

[PX]_(F) : The concentration (% by weight) of p-xylene in the threexylene isomers in the feed stock.

[PX]_(P) : The concentration (% by weight) of p-xylene in the threexylene isomers in the product.

[PX]_(E) : The equilibrium concentration (% by weight) of p-xylene inthe xylene isomers at the reaction temperature.

[EB]_(F) : The concentration (% by weight) of EB in the feed stock.

[EB]_(P) : The concentration (% by weight) of EB in the product.

[X]_(F) : The concentration (% by weight) of the three xylene mixtisomers in the feed stock.

[X]_(P) : The concentration (% by weight) of the three xylene isomers inthe product.

EXAMPLE 6

The powdery catalysts B-5, D-2, E, E-1 and F-1 obtained in Example 1were molded, calcined and reduced in the same way as in the catalysts Aand A-2 described in Example 5, and used in the isomerization of xyleneunder the same reaction conditions in the same reactor using the samestarting material as in Example 5. The various data obtained after alapse of 70 hours from the initiation of feeding were as shown in Table6. The definitions of these data are the same as in Example 5.

It is seen as in Example 5 that when Ba, In, Ti and Cd were added, (1)the isomerization activity and the deethylation activity of Pt are notdegraded, and (2) the activity of hydrogenating the benzene ring anddemethylating xylenes is inhibited.

                  TABLE 6                                                         ______________________________________                                                  Catalyst                                                                            B-5                                                                     E     (Pt,    E-1     D-2   F-1                                               (Pt)  Ba)     (Pt, In)                                                                              (Pt, Ti)                                                                            (Pt, Cd)                                ______________________________________                                        PX approach to                                                                            100.9   102.0   103.0 101.6 102.3                                 equilibrium (%)                                                               EB decomposition                                                                          60.2    52.3    50.5  46.2  52.0                                  ratio (%)                                                                     Xylene loss (%)                                                                           5.59    3.93    1.53  1.23  1.32                                  EB decomposition                                                                          10.8    13.3    33.0  37.6  39.4                                  ratio/xylene loss                                                             Deethylation ratio                                                                        91.4    80.8    83.6  87.6  85.2                                  (%)                                                                           Amount of de-                                                                             7.32    10.22   5.43  5.55  3.88                                  methylation (mmol)                                                            Amount of C.sub.6 +                                                                       3.18    0.54    0.08  0.39  0.05                                  naphthenes formed                                                             (wt. %)                                                                       C.sub.6 naphthenes/                                                                       21.40   3.09    0.59  3.34  0.27                                  benzene (wt. %)                                                               ______________________________________                                    

EXAMPLE 7

Benzene was hydrogenated in a fixed bed reactor using the same catalystsA, A-2, B-5, D-2, E, E-1 and F-1 as described in Examples 5 and 6. Thereaction conditions were as follows:

Temperature: 200° C.

Weight hourly space velocity: 8.0 hr⁻¹ (based on the weight of zeolite)

Hydrogen/benzene mole ratio: 1:1

Pressure: atmospheric pressure

Feed stock: 99.98 wt. % benzene

The conversion of benzene in 2 hours after the initiation of feeding isshown in Table 7.

FIG. 1 of the accompanying drawings shows the relation between theamount of liquid non-aromatics (at least 99 wt. % of which consisted ofC₆ naphthenes) formed by the hydrogenation of benzene under theaforesaid reaction conditions at atmospheric pressure and the amount ofthe hydrogenation products (C₆ ⁺ naphthenes) of xylenes obtained in theisomerization of xylenes under the reaction conditions at elevatedpressure described in Examples 5 and 6. A positive correlation is seenbetween the two. This shows that the metal (b) which inhibits theformation of naphthenes during the isomerization of xylenes underelevated pressure inhibits the hydrogenation of benzene at atmosphericpressure.

                  TABLE 7                                                         ______________________________________                                                               Non-aromatics                                                        Type of  in the product                                         Catalyst      metal (b)                                                                              (wt. %)                                                ______________________________________                                        A             None     10.90                                                  E             None     4.86                                                   A-2           Sn       0.45                                                   B-5           Ba       0.25                                                   D-2           Ti       0.24                                                   E-1           In       0.11                                                   F-1           Cd       0.05                                                   ______________________________________                                         Non-aromatics in the product: only liquid nonaromatics without gaseous        nonaromatics.                                                            

EXAMPLE 8

The powdery catalysts described in Table 8 which were obtained inExample 1 were molded, and calcined in the same way as in Example 5. Inan fixed bed reactor, the same benzene as used in Example 7 washydrogenated under the same reaction conditions as shown in Example 7.The results are shown in Table 8.

As in seen from Table 8, the addition of the metals (b) leads to theinhibition of the activity of hydrogenating the benzene ring. It isclear from FIG. 1 that the amount of C₆ ⁺ naphthenes in the xyleneisomerization products decreases, and the loss of xylenes can bereduced.

                  TABLE 8                                                         ______________________________________                                                    Type of  Liquid non-aromatics                                     Catalyst    metal (b)                                                                              in products (wt. %)                                      ______________________________________                                        A           None     10.90                                                    A-1         Ge       1.98                                                     A-3         Pb       4.89                                                     A-4         Cr       2.59                                                     A-5         Mo       2.88                                                     A-6         W        5.23                                                     A-7         Os       4.09                                                     A-8         Pd       4.04                                                     B           None     7.92                                                     B-1         Sr       2.80                                                     B-2         Br       4.26                                                     B-3         Ga       2.20                                                     B-4         Ce       4.40                                                     C           None     1.05                                                     C-1         Y        0.74                                                     C-2         Zr       0.65                                                     D           None     3.37                                                     D-1         Zn       2.46                                                     E           None     4.86                                                     E-2         La       1.46                                                     G           None     5.55                                                     G-1         Hg       0.79                                                     ______________________________________                                    

EXAMPLE 9

Xylenes were isomerized at atmospheric pressure using the catalysts asused in Example 8.

The catalysts were calcined and reduced in the same way as described inExample 8. The reaction conditions were a temperature of 380° C. and aWHSV of 6 for the catalysts B and B-1, and a temperature of 350° C. anda WHSV of 8 for the other catalysts. The other reaction conditions werethe same as in Example 8, and the feed stock was the same as that usedin Example 5.

After a lapse of 20 hours from the initiation of the feeding, thecharacteristic values of the reaction defined in Example 5 were as shownin Table 9.

It is seen from Table 9 that when the metals (b) shown in Table 9 areadded to the platinum-ZSM-5 catalyst, the following effects can beobtained.

(1) The ability of the catalyst to isomerize xylenes is retained almostcompletely.

(2) The ability of deethylating ethylbenzene, which is inherent toplatinum, is not degraded.

(3) The activity of platinum itself to demethylate xylene is inhibited.

Taken together with the fact shown in Example 8, it is evident that byadding the metals (b) shown in Table 9 (the same as those shown in Table8) to the Pt-ZSM-5 catalyst, there can be obtained catalysts forisomerization of xylenes, which greatly reduce the loss of xylenes.

                                      TABLE 9                                     __________________________________________________________________________                    EB decom-     Deethyl-                                                                           Demethyl-                                           PX approach                                                                          position                                                                            Xylene  ation                                                                              ation                                           Metal                                                                             to equili-                                                                           ratio (A)                                                                           loss (B)                                                                              ratio                                                                              ratio                                      Catalyst                                                                           (b) brium (%)                                                                            (%)   (%)  A/B                                                                              (%)  (%)                                        __________________________________________________________________________    A    None                                                                              98.8   51.6  1.45 35.6                                                                             94.1 64.9                                       A-1  Ge  99.8   52.5  0.98 53.6                                                                             93.9 46.2                                       A-3  Pb  98.9   40.5  0.52 77.9                                                                             90.8 18.5                                       A-4  Cr  98.4   41.9  0.56 74.8                                                                             91.6 32.4                                       A-5  Mo  99.2   39.1  0.55 71.1                                                                             88.5 23.2                                       A-6  W   99.7   42.5  0.58 73.3                                                                             90.9 26.3                                       A-7  Os  99.5   49.0  0.83 59.8                                                                             94.0 44.8                                       A-8  Pd  100.3  48.0  1.12 42.9                                                                             93.5 62.5                                       B    None                                                                              100.8  90.0  4.77 18.9                                                                             98.7 62.3                                       B-1  Sr  101.0  80.2  2.58 31.1                                                                             98.7 58.1                                       B-2  Be  101.3  43.0  0.84 51.2                                                                             90.4 40.7                                       B-3  Ga  100.8  32.7  0.53 61.7                                                                             90.7 13.4                                       B-4  Ce  100.9  51.6  0.98 52.7                                                                             93.9 41.5                                       C    None                                                                              100.9  46.8  0.86 54.4                                                                             91.9 37.0                                       C-1  Y   100.9  48.6  0.71 53.4                                                                             91.8 38.3                                       C-2  Zr  101.1  51.0  1.00 51.0                                                                             92.7 38.4                                       D    None                                                                              100.9  45.6  0.86 53.0                                                                             93.1 42.9                                       D-1  Zn  100.1  35.4  0.48 73.8                                                                             88.0 29.1                                       E    None                                                                              98.4   46.3  0.87 53.2                                                                             93.3 66.0                                       E-2  La  99.5   43.1  1.22 35.3                                                                             85.9 33.6                                       G    None                                                                              97.3   43.2  0.62 69.7                                                                             91.3 53.3                                       G-1  Hg  94.5   40.8  0.60 68.0                                                                             89.4 51.0                                       __________________________________________________________________________

EXAMPLE 10

Chromatographic alumina gel (300 mesh) was added to each of the powderycatalysts H-1 and H-2 obtained in Example 1 in a weight ratio of 1:1.They were fully mixed and molded into a product having a size of 10 to20 mesh. The molded product was calcined in air at 450° C. for 8 hours,and subsequently, reduced in a stream of hydrogen at 400° C. for 2hours.

Benzene was hydrogenated using the resulting catalyst by the same methodand under the same conditions as described in Example 7. The conversionfor benzene in 2 hours after initiation of feeding was as shown in Table10. Subsequently, xylenes were isomerized by the same method and underthe same conditions as described in Example 9. The characteristic valuesof the reaction after a lapse of 5 hours from the initiation of feedingwere as shown in Table 11. The definitions of the characteristic valuesof the reaction were the same as those given in Example 5.

It is seen from Table 11 that when the Sn/Pt atomic ratio is too low,the effect of inhibiting the activity of hydrogenating the benzene ringis insufficient, and on the other hand, if it is too high, theactivities of isomerizing xylenes and decomposing ethylbenzene decrease.

                  TABLE 10                                                        ______________________________________                                        Catalyst             H-1    H-2                                               ______________________________________                                        Sn/Pt atomic ratio   0.33   3.3                                               Conversion of benzene (%)                                                                          14.1   0.3                                               ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                        Catalyst               H-1    H-2                                             ______________________________________                                        PX approach to equilibrium (%)                                                                       99.2   90.5                                            EB decomposition ratio (%)                                                                           45.5   34.5                                            Xylene loss (%)         0.58   0.31                                           Deethylation ratio (%) 91.1   85.8                                            Demethylation ratio (%)                                                                              29.0   --                                              ______________________________________                                    

What we claim is:
 1. A catalyst composition comprising(i) a crystallinealuminosilicate selected from the group consisting of zeolite ZSM-5,zeolite ZSM-11, zeolite ZSM-12, zeolite ZSM-35 and zeolite ZSM-38 andhaving a silica/alumina mole ratio of 20 to 1,000; and (ii) at least twometals which are(a) platinum and (b) at least one other metal selectedfrom the group consisting of titanium, barium, and lanthanum.
 2. Thecomposition of claim 1 wherein the amount of platinum is 0.001 to 2% byweight based on the weight of the aluminosilicate.
 3. The composition ofclaim 2 wherein the amount of platinum is 0.005 to 1.5% by weight basedon the weight of the aluminosilicate.
 4. The composition of claim 1wherein the atomic ratio of platinum to the other metal (b) is in therange of from 1:0.01 to 1:10.
 5. The composition of claim 4 wherein theatomic ratio of platinum to the other metal (b) is in the range of from1:0.05 to 1:5.
 6. The composition of claim 1 wherein thealumino-silicate has a silica/alumina ratio of from 30 to
 200. 7. Thecomposition of claim 1 wherein the alumino-silicate is zeolite ZSM-5. 8.The composition of claim 1 which has a cyclohexane/n-hexane sorptionratio of not more than 0.95.
 9. The composition of claim 8 which has acyclohexane/n-hexane sorption ratio of not more than 0.8.
 10. Thecomposition of claim 1 which has an activity index of not less than 100.11. The composition of claim 10 which has an activity index of not lessthan
 100. 12. The composition of claim 1 which has a hydrogenation indexof not more than 6%.
 13. The composition of claim 12 which has ahydrogenation index of not more than 2%.
 14. The composition of claim 1which further comprises a refractory inorganic oxide as a binder. 15.The composition of claim 14 wherein the amount of the refractoryinorganic oxide is 1 to 99% by weight based on the weight of thecomposition.
 16. The composition of claim 1 which is in the form ofpellets or tablets.
 17. The composition of claim 2 wherein the atomicratio of platinum to the other metal (b) is in the range of from 1:01 to1:10.
 18. The composition of claim 1 wherein the other metal (b) istitanium.
 19. The composition of claim 1 wherein the other metal (b) isbarium.
 20. The composition of claim 1 wherein the other metal (b) islanthanum.